This article is a news flash about the full Commit Digest, which is "a weekly overview of the development activity in KDE." A little poking around reveals more about KDM and SDDM. Someone may be by later to explain further.

There is not yet a chosen replacement, but any login manager can be used. The currently most promising options are LightDM and SDDM. We've investigated the situation during a recent sprint, and briefly discussed the result on the Plasma mailinglist, you can find the thread here.

Not having kdm on top of Frameworks 5 is not an immediate problem (of course one can still use KDM from KDE SC 4.x).